EASY FIX ON ERROR “550 5.7.1 authentication required”

Table of Contents

Mail clients like Outlook, Thunderbird, etc, make communication easier.

At times, these email clients throw up errors like “550 5.7.1: authentication required” resulting in email failure.

Email users will be confused when they can’t figure out the exact reason for the auth failure.

That’s why we get frequent requests from customers to solve mail errors as part of our Server Management Services.

Today we’ll see the error in detail and discuss how our Support Engineers fix this error.



What is Error: “550 5.7.1 authentication required”?

Firstly, let’s have a deep look at the exact error.

This mail authentication error has three parts:

  • 550 5.7.1 authentication required” indicates reply code, status code and reply text respectively.
  • Error 550 is an email error code that indicates the user’s improper authentication to the server. Email errors that start with ‘5’ require an action instead of a retry.
  • 5.7.1 indicates a message refused error. Again, “authentication required” is the human-readable form of the resulted error.

In short, the error “550 5.7.1 authentication required” is a permanent failure that occurs due to incorrect credentials provided by the user.

Why does it happen?

We now know the details of the error. It’s time now to check on why it happens.

Email security is of much importance while sending any sensitive information. The absence of account validation could lead to attacks from spammers who use the server to send unnecessary emails. Spamming from the server will end up in email server blacklisting too.
Therefore, server administrators always allow emails only from authenticated senders. And, when authentication fails, server reports error.

There are two possibilities for this auth failure error.

1. Incorrect login details

Some users give incorrect user name and password while configuring an Email client. This can be typing errors like extra space, typo errors in entering user details, etc.

When the server identifies the connection from a non-existing user, it automatically denies the mail sending with an error.

2. Configuration details of Email client

Usually, incorrect mail client configuration can also result in Email errors. The configuration details vary for different Email clients. For mails to work, the user should enable the option for authentication in every email client.

Therefore, we always ask customers to check the configuration details in email clients.

How we fix error “550 5.7.1″?

Curious to know the fix?

When this error happens, our Support Engineers begin the investigation by checking the mail server logs. For example, in a cPanel Exim server, we check the logs at /var/log/exim_mainlog.

This gives us a clue on exactly what has gone wrong with the email client configuration. Generally, the incorrect credentials, typo errors, extra spacing, etc. will be readily viewable from logs.
If we find mistakes, we suggest the users double-check the given credentials like email username and password in the mail client.

Similarly, not enabling the SMTP authentication in email clients could also cause the same error.

For users configuring Outlook, we suggest the following steps to enable the SMTP authentication. Move to Account Settings>>More settings>> Outgoing server
There is an option to enable “My outgoing server (SMTP) requires authentication”. Enable it and results would appear as:

[No luck in solving email errors? Seek expert help here.]


In short, error “550 5.7.1 authentication required” occurs as a result of providing incorrect credentials or due to not enabling SMTP authentication in the mail client.
Today we discussed the various causes of the error and how our Support Engineers fix it.

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